Genotoxic chemicals are an existing wide-spread health hazard to the human population. Advances in genetic toxicology testing have made it possible to assay potential mutagens, carcinogens, teratogens and clastogens in the environment. However, many currently available mammalian cell tests are costly, time consuming and labor intensive. This research program is directed toward the application of high-speed flow cytometry (FCM) to expedite genetic toxicology testing using mammalian cell systems. The flow cytometer is able to analyze more than 100,000 cells/minute, and thus should be able to provide 1) faster analysis of target cells, 2) larger populations of cells for better statistics, 3) the potential for automating mammalian cell tests, and 4) potential for lowering the overall cost of mammalian cell tests. During Phase I of this program, FCM will be used to automate the cell and data processing aspects of the agents to cause chromosomal aberrations in target cells. With the currently available method, cell counts are obtained on a relatively small percentage of the total cell population. FCM will make it possible to increase the number of cells counted in the micronucleus assay 200-300 times, compared to the manual method. Phase II will apply FCM to additional mammalian cell testing protocols. FCM automation has far-reaching commercial applicability for toxicological testing.